Nb3Al superconductors

Recent progress of Nb3Al superconductors is described. A large-current conductor of 46 kA at 13 T, produced from a jelly-roll (JR) Nb/Al composite by a direct diffusion-process, is about to be tested as an insert-coil conductor for fusion magnets. The 1 GHz NMR magnet has given a motivation to do an entirely new approach to Nb3Al processing that allows a dramatic improvement in high-field J(c) characteristic. The RHQT process produces a stoichiometric Nb3Al with fine-grain structures via a lice supersaturated solid solution and, hence, large J(c) over the whole range of magnetic fields. Controlling a heating temperature within a narrow region of extended bee solid solution ensures the room-temperature ductility of as-quenched wires and homogeneous J(c) characteristics of transformed Nb3Al along the long piece-length. A solenoid coil fabricated by a wind-and-react method, with Cu clad RHQT Nb3Al conductors, could generate an additional 1.3 T at 2.1 K in a bias field of 21.2 T, and was operated in a persistent-current mode without a bias field. The variants of RHQT process (TRUQ, DRHQ, Cu-added RHQO) improved significantly the high-field J(c) without sacrificing the strain tolerance.